In rotary machines such as steam turbines, seals are provided between rotating and stationary components. For example, in steam turbines, it is customary to employ a plurality of arcuate packing ring segments (bearing labyrinthian features) to form a labyrinth seal about and between stationary and rotating components. Typically, the arcuate packing ring segments are disposed in an annular groove in the stationary component concentric about the axis of rotation of the machine, and hence concentric to the sealing surface of the rotating component. The sealing function is achieved by creating turbulent flow of a working media, such as steam, as it passes through the relatively tight clearances within the labyrinth defined by the seal face teeth and the opposing surface of the rotating component.
In order to avoid damage to the rotor and packing ring during transient conditions such as startup and shutdown, variable clearance packing rings have been used. Variable clearance packing rings typically employ springs that bias and hold the ring segments in large clearance positions during transient conditions. When disposed in large clearance positions, seal faces carried by the packing rings are spaced substantially outwardly of the rotary component, avoiding contact between the segments and rotor. At machine start-up the working fluid medium (steam) within the grooves of the stationary component is pressurized. Presence of the pressurized medium within the grooves causes a pressure build up. This pressure build up urges the segments to move inwardly against the bias of the springs, towards inner or small clearance positions. When the pressure in the groove overcomes the opposing bias of the springs, the seal faces of the segments create a desired labyrinthian seal with the rotor.
Springs used to bias the segments into the large clearance positions are typically located within the annular groove, disposed between a hook portion of the packing ring segment and a locating flange of the casing. Springs disposed in this relatively small region of the annular groove can be difficult to install, particularly in smaller turbine units. In addition, a large hook portion relative to the dimensions the other ring components is required. This small region and large hook portion can make ring-casing assembly difficult. Thus, it would be desirable to dispose the biasing spring in a more spacious region of the groove, allowing for a less cumbersome hook portion, and easier ring-casing assembly.